1. Cross-Reference to a Related Application
Reference is made to commonly assigned copending U.S. Pat. application Ser. No. 420,000, filed simultaneously herewith in the name of Douglass L. Blanding and entitled ELECTROPHOTOGRAPHIC FILM CORE DEVICE.
2. Field of the Invention
The present invention relates to electrophotographic copying or printing machines and, more particularly, to means for supporting a film core and the elements directly associated therewith.
3. Description Relative to the Prior Art
Many electrophotographic copiers or printers employ an endless photoconductor belt rather than a photoconductor drum and the device that carries the photoconductor belt, including the belt-supporting rollers, commonly referred to as a film core.
As is well known in the prior art relating to electrophotographic copying or printing machines, each transverse region of the photoconductor belt moves successively past a number of stations, which typically include: a charging station where an electrical charge is applied; an exposure station where an image is focused on the belt to selectively discharge the electrical charge and produce a corresponding electrostatic image on the belt; a toning station where a toner material is applied to the belt to produce a toned image; a transfer station where the toned image is transferred to a receiver sheet or web; and, a cleaner station where the belt is cleaned and electrically neutralized in preparation for the next operational cycle. In some cases, such as color copiers, several toner stations are employed and the process is repeated to superimpose different colored images on the receiver.
In such a machine, it is important for accurate spacing to be maintained between the photoconductor belt and cooperating elements of the various stations described above. For example, in such machines in which the image is focused on the belt from a light-emitting diode write-head, the depth of focus of the image is very small and must be accurately coincident with the belt surface to produce a sharp image on the belt, which requires correspondingly accurate support of the write-head assembly relative to the adjacent portion of the belt. The criticality of such spacing depends somewhat on the type of station involved, but is an important consideration for most or all of the various stations.
In many electrophotographic copying or printing machines known in the prior art, the film core and the various stations associated with it are all mounted to the frame or housing of the machine and, while they may be adjustable relative to the frame or housing and to each other, they are all rigidly connected to the frame or housing once such adjustments have been made. Consequently, any subsequent distortion of the frame or housing imparts corresponding distortion or displacement to the film core and/or to the various stations, and can therefore negate previous adjustments. Similarly, if the film core itself is distorted following such adjustments, it is inevitable that its cooperation with one or more stations will be impaired.
In some constructions in which the film core is supported rigidly with respect to the machine frame, one or more of the various stations is positioned by the film core itself, which tends to alleviate the foregoing problem. However, it is impractical to locate the transfer drum in this manner because of its relatively large size and mass. Furthermore, distortion of the machine frame can still impart corresponding distortion to the film core itself, thereby influencing the transverse or lateral position of the belt with respect to the various stations. If the frame imparts distortion to the film core in a dynamic or periodic fashion, for example because of a vibrational harmonic in the machine, even a belt-tracking mechanism employing a sensor and a servo operated belt steering system may not be able to compensate for such influences.